The Sky (15-14) have made the playoffs in each of coach James Wade's three seasons with the team.
Kahleah Copper scored 14 points and Candace Parker had 12 points, 13 rebounds and eight assists for Chicago.
Kelsey Plum led the Aces (20-8) with 23 points. A'ja Wilson scored 18 points and grabbed 12 rebounds and Williams finished with 14 points.
Liz Cambage (COVID protocol) and Dearica Hamby (ankle) did not play for Las Vegas.